This invention relates generally to gas turbine engine nozzles and more particularly, to methods and apparatus for sealing gas turbine engine nozzles.
At least some known gas turbine engines include an exhaust nozzle including a variable geometry system. The variable geometry system adjusts an area of the exhaust nozzle through the use of flaps and seals. The flaps define discrete sectors of the flowpath, and the seals form the remaining flowpath between adjacent flaps. Because the exhaust nozzles are subjected to high temperatures and thermal gradients as a result of hot combustion gases exiting the engine, the variable geometry system must maintain a coherent flowpath while shielding the structural components of the variable geometry system.
At least some known flap and seal systems consist of a backbone and a basesheet construction. The backbones secure the basesheets within the variable geometry system. The flaps and seals are conventionally arranged such that each seal basesheet extends over a portion of the flap basesheet thus shielding the flap edges from hot combustion gases exiting the engine. Accordingly, a center portion of each flap basesheet is unshielded and exposed to the combustion gases. During engine operation, the flap basesheet edges are exposed to less heat than the center portion of the basesheet, and as a result, a circumferential thermal gradient may be induced to the basesheet. Continued operation with the thermal gradient may induce thermal stresses into the basesheet which over time, may lead to warping, thermally induced distortion, cracking, or premature failure of the flaps.
To facilitate reducing thermal stresses induced to the flaps, at least some known engines include a xe2x80x9cfloatingxe2x80x9d basesheet design. More specifically, within such designs, a unitary basesheet is used to establish a portion of the flowpath. Because the basesheet is not rigidly coupled to the backbone, the basesheet may thermally expand more than the backbone, thus facilitating reducing thermal gradients in comparison to designs having basesheets that are attached rigidly to or formed integrally with the backbone. However, because the center portion of the associated flap basesheets are still exposed to the hot combustion gases, thermal gradients between the basesheet edges and basesheet center portion may cause warping, cracking, or thermally induced distortion within the flap assembly.
At least some other known engines include a longitudinally segmented basesheet design which has a central portion connected to the edge portions by channels which are crimped on the basesheet. The channels extend across and are attached to a backside of the basesheet and facilitate reducing thermally induced stresses by permitting differential thermal growth of the predominately cold portion of the seal assembly and the predominately hot portion of the segmented basesheet. However, aligning the basesheets while attaching the channel to the backside of the basesheets may be time consuming. Furthermore, because the channel is attached across the basesheet and between the edges of the basesheet, continued thermal cycling may create local stress concentrations between the channel and the basesheet.
In one aspect, a method for assembling a flap system for a gas turbine engine exhaust nozzle including a plurality of backbone and basesheet assemblies is provided. The method includes providing a flap basesheet having a width defined between a pair of side edges that are coupled together by a leading edge and a trailing edge, and including at least one stiffener that extends between the basesheet side edges and includes an intermediate portion that has a width that is smaller than that of the basesheet and is at least one of bonded to and formed integrally with the basesheet, and coupling the basesheet to the gas turbine engine with a backbone assembly.
In another aspect, a flap basesheet assembly for a gas turbine engine exhaust nozzle is provided. The basesheet assembly includes a body and at least one stiffener. The body includes a first side edge and a second side edge coupled together by a leading edge and a trailing edge. The body has a width extending between the first and second sides. The at least one stiffener extends across the body between the first and second edges and includes an intermediate section that has a width smaller than that of the body width. The intermediate section of the stiffener is at least one of integrally formed with and bonded to the basesheet assembly body.
In a further aspect, a gas turbine engine including a variable engine exhaust nozzle including a flap basesheet system coupled to the engine exhaust nozzle is provided. The basesheet system includes a body and at least one stiffener. The body includes a first side edge and a second side edge that are coupled at a leading edge and a trailing edge. The body has a width defined between the first and second sides. The at least one stiffener extends across the body between the first and second edges. The stiffener includes an intermediate section that has a width that is smaller than the body width. The stiffener intermediate section is at least one of integrally formed with and bonded to the basesheet assembly body.